Tuesday, August 14, 2012

LROC: Giant flow of Tycho impact melt

This giant fossilized glacier of impact melt extends north from a much larger mass
of impact melt of the north rim of Tycho. This single
section of the flow is more than 10 kilometers long. LROC Narrow Angle Camera (NAC) observation M185954551R, LRO orbit 12482, March 9, 2012; resolution is 0.6 meter per pixel of a 43.53° angle of incidence, from 64.8 kilometers altitude. View the larger LROC Featured Image HERE
[NASA/GSFC/Arizona State University].

Jeffrey Plescia

LROC News System

Impact melt is formed during the crater excavation process due to the intense heating of the target rocks. Some of the melt is ejected from the crater and deposited on the rim. In this case, on the north rim of Tycho, not far from the Surveyor 7 landing site, a large amount of melt was deposited, pooled and then flowed downslope away from the crater. This flow (41.162°S, 348.605°E) is about 21 km from the northern rim. Upslope, toward the rim, there are also numerous smaller pools of impact melt (now frozen to solid rock). Contrast this flow with the River of Rock on the southeast side of Tycho crater.

From a half-sized reduction of the original LROC context image (HERE), this expanded view of the full LROC frame (NAC M185954551R) shows more of the flow anatomy, extending north from Tycho. The
white box shows the field of view included in the featured image above
[NASA/GSFC/Arizona State University].

This giant frozen flow is more than 10 km long! When the flow emerged onto the plains it was about 1.3 km wide; at the terminus it spread out about twice as wide (2.7 km). Along the center of the flow is a channel with levees; the channel is about 1 km wide. In the levee walls and on the flanks of the flow are layers which formed when surges of melt spilled over onto the side of the flow. The morphology of the end of the flow, with lobes stepping to the right, indicates that with each surge, the end of the flow was directed eastward. The surface within the channel shows tension cracks that are perpendicular to the flow direction and formed as the solidified crust fractured. There are several other flows of impact melt on the northern flank, although this is the most dramatic. Impact melt also fills much of the crater floor.

The very successful and daring Surveyor 7 was successfully landed right in the middle of the complex Tycho impact melt fields, north of the crater, about 10 km away from the field of view included in the LROC Featured Image. Less than a kilometer, beyond view of the spacecraft's cameras, is s substantial melt pool, where Surveyor might easily have landed instead. LROC NAC M152952815R, LRO orbit 7674, February 21, 2011, resampled from the original resolution of 0.5 meters from 44.7 kilometers [NASA/GSFC/Arizona State University].